1. Field of the Invention
The present invention relates to the recovery and/or separation of nickel and cobalt from acidic aqueous solutions and more particularly to the recovery of nickel and/or cobalt from acidic leach solutions by mixed organic extractants.
2. Prior Art
There are many processes for recovering nickel and cobalt from acidic aqueous solutions. These processes can be categorized generally as precipitation (including hydrogen precipitation), cementation, crystallization, electrolysis and organic phase extraction. Most, if not all, of these processes require substantial neutralization of any free acid contained in the aqueous solution to increase the rate and extent of nickel and/or cobalt recovery. Free acid neutralization significantly increases overall process capital and operating costs. The additional equipment required for neutralization increases capital costs, and increased consumption of sulfuric acid, neutralization reagents and by-product disposal all add to the operating costs.
An example of liquid extraction processes requiring neutralization is that described in French Pat. No. 2,236,948. The process described in this French patent extracts nickel and cobalt from acidic aqueous solution with a liquid organic extractant containing a carboxylic acid, a hydroxyoxime and a sulfonic acid, as a phase dispersant all of which are dissolved in a nonpolar solvent. The pH of the nickel-and/or cobalt containing aqueous solution is maintained at a value above 2.5. There is nothing in the French patent that would suggest that nickel and cobalt could be selectively extracted at pH values below 2.5, and advantageously at pH values of 2.0 or less.